Study: No Link Between Mercury in Fish, Heart Disease

March 23, 2011 -- Fish lovers trying to stay heart-healthy can mostly relax about the mercury in fish, according to a new study.

Mercury exposure from eating fish, linked in some previous research to a higher risk of cardiovascular disease, does not appear to boost heart disease risk, the new study suggests.

“We didn't see any evidence that higher levels of mercury were linked to higher cardiovascular harm," says researcher Dariush Mozaffarian, MD, DrPH, an associate professor of medicine and epidemiology at Brigham and Women's Hospital and Harvard Medical School, Boston.

''At exposure levels commonly seen in the U.S., we didn't see any evidence of harm," he tells WebMD. Mozaffarian cautions that his study, which followed nearly 7,000 men and women, was in adults only and that caveats about limiting intake of high-mercury fish still hold for pregnant women, nursing mothers, and children.

However, the new research is good news for others who eat seafood in moderation, another expert says. "It's reassuring that mercury [from fish] does not appear to be a major cause of cardiovascular disease, based on this major study," says Gina Solomon, MD, senior scientist at the Natural Resources Defense Council. The environmental action group has studied mercury in fish and posts a guide on its web site detailing how to eat fish more safely.

The study findings are reported in The New England Journal of Medicine.

Mercury Exposure and Heart Disease: Background

Eating fish, with its heart-healthy omega-3 fatty acids, has been linked with reduction in heart disease and stroke, Mozaffarian writes.

But fish is also a major source of mercury exposure, and chronic low levels have been linked with brain development delays in infants. That has triggered advice that intake of fish high in mercury be avoided in women who are pregnant or nursing and in children.

But in adults who aren't pregnant or nursing, the main concern has been a potential for cardiovascular toxicity.

Previous research has produced conflicting findings, Mozaffarian tells WebMD, so he conducted the new study.

Mercury Exposure and Heart Disease: Study Details

Mozaffarian and colleagues evaluated data from two large studies that included more than 51,000 men from the Health Professionals Follow-up Study (begun in 1986) and more than 121,000 women enrolled in the Nurses' Health Study (begun in 1976).

Every two years, the participants answered questions about their medical history, risk factors, disease, and lifestyle.

The researchers zeroed in on 3,427 participants who did not develop heart disease during the follow-up and another 3,427 who did. Mercury levels were evaluated from toenail clippings the participants provided. Toenail clippings are an excellent biomarker for mercury, Mozaffarian says, because mercury binds tightly to the protein in the toenail.

They also evaluated levels of selenium, a trace nutrient some think protects against mercury toxicity, in the clippings.